Signaling system



March 12, 1946.

l W. VAN BROBERTS SIGNALING SYSTEM 2 Sheets-Sheet 1 Filed April 29, 1943 lil . Smid INVENTOR /,/4/v l? seri. BY )flw ATTORNEY Malldfl 12, 1946 w. vAN B. ROBERTS 2,396,288

SIGNALING SYSTEM 'Filed April 29, 1943 2 sheets-sheet 2 T11-1.4L 'A sclLLasroP/s ATTORNEY Patented Mar. 12, 1946 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Walter van B. Roberts,v Princeton, N.-J., assigner to Radio Corporation. of America, a corporation of Delaware ApplcationApril :29; 1943, 4,Serial No. 484,972

17 Claims.

This i invention relates primarilyv to *means for' tion of time, .a second voltage which is a sinusoidal function of E, for example, `Em sin KEwhere K is aconstant and Em isthe amplitude of said sinusoidal voltage;

Another object is .to recreate, from a-pair of sinusoidal voltages.` such' as Em sin KE and Em cos KE,.the voltageE of whichsaid pair are functions.

A particular object is to utilize-said pair oi voltages'as modulation voltages in a transmission system, whereby a predetermined degree of modulation. is never exceeded for any value of the first voltage E, and whereby transmissions of vsuch system are notintelligibly receivable on conventional receivers.

.Fig l shows means for producing from a given voltage E two voltageswhich. are a sinusoidal function vof the given 'voltage and Ameans to proa-- duce from .the two sinusoidal voltages the'given' voltage E,

Fig. 2 shows an embodiment of a' signalingV systemwherein the means .of Figure. lare used to supply as modulating `potentials .thetwo produced voltages, whereby a given .degreeof modulationV is never exceeded for any value .of the given 'volt-f age andwherein a novel receiver isusedto receive thetransmitted signal and reconstruct therefrom the given voltage.

Fig. 3 shows a laboratory; applicationfof part of the arrangement of Fig. `1.

Fig. 4av shows means for theproduction .and

use of a rotary eld, by means ofthe twovoltages derived from the .given voltage.

Fig. 4b shows means for the production `ofla rotary electric field applied to an oscilloscope..

Referring to Fig. 1, E is a source of voltage` whose instantaneous value is V,any arbitrary func` tion of` time, such as the complex waveform of voltage representative of speech. S is a.source` of alternating voltage of' frequency which is high compared to anyfcomponent frequency olfthe voltage E. PM is a phase modulator upon which voltage from E and S are impressed and whose output is therefore avvoltage 'similar to the voltage fromv S except that .it is phase modulated in accordancewi'th. E.. The output of the phase modi uIator PM^ iisiy subjected to `vfrequencyl multiplica;

tion in EHG' whereby the amount of 7phase modular-- tion is. greatlyincreased, preferably -to such extent that the Vphase 'deviation' reaches manyv radians.

This -stronglyph'ase modulated vrwave is then impressed on.a(preferably-pushpulD detecting systemD, for example,the upper one, as show-n. Meanwhile.. some of 'the unmodulated voltage fromzS has! vbeen lequally multiplied :in frequency in HG. and subjected .tophasetadjustment vin PS and `applied...copliasably tothev detectors D, also asxshown; If this'. latter. voltage is y made large compared to. thelpl'iase-.modulatedV voltage and if itsqphaseon ithe..detector 'is ladjusted to be in quadrature with the .phase .'offthemodulatedvolt# age. on' AD when. `theimodulating :voltage Eis zero,- thenzit is .evident thatthe amplitude .ofzthe out-` put of thepairof detectorswillyary as the sine.`

of the; phase deviation',` of the .modulated .voltage and hence will beEm .sin KE,.thus.fulfil1ing`the rst 'object of the invention.;V

A duplicate detecting; system D' is .farranged'in parallel with thefabove ;described.system, but in this latter detecting system the unmodulated (from HG'.) voltage Aphase is'. adjustedin. .PS. to.

be..90" .differentfrom .that employed zin `the .first detecting system D, wherebyth'e outputofth'e:

secondsystemzis Elm cos:KE.I

It should. .bei noted. that; other phases fof. the: detector "output voltagesare obtainable :by/other adjustments ofthe Shifters: `but that for mostV purposes.A it is .onlynecessary to iarrange that the. unmodulated. `voltagesapplied to `the two ldetecting, systems bein quadrature-with eachother,

which insuresfthat one* of. the. output voltages. is aan extremum when therotheris zero, and vice versa. Itlis also possible rto dispense withoneof therectifers'in each of the` systems DA and ..D`

for-many purposes,- especially; when a direct our; rent component inthe output is .not objectionable.

Also, other equivalent methods of energizingthe.

detectors may be employed equally well, but need not be described` as such variationsV are well known..-

To` .recapitulate, ,the dotted rectangle marked- SI O.` G.' has twopairsof output terminals and one pairof input .terminalsfand converts an arbitrarily varying input voltage .E toa pair of-output voltages each varying` sinusoidally with respect to lil-'which' are expressible as Emi sin (KEl-Pi)4 andEmz cos `(KE+P2`) where K is a. constant equal to thephasedeviaton sensitivity of the,

modulator PM"multipliedzbyV the amount offre. quencymultiplication` employed, `and Em and P` arel constants determined by the circuit amplification and thephaSe-shftcr adjustments respeta.`

tively. Ordinarily Emi and Emz will be made equal, say Em, while P1 and P2 will be equal and preferably zero.

The other dotted rectangle of Fig. 1, marked I. S. G., shows inverse sinusoidal generating means to undo what the sinusoidal output generator device S. O. G. has done to the input voltage El. That is, the I. S. G. device has two pairs of input terminals and one pair of output terminals, and if voltages Em sin KE and Em cos KE are applied to the input terminals, a voltage proportional to E will be obtained at the output terminals. The I. S. G. device comprises a pair of balanced modulators BM and BMi, a frequency modulation detector FM, an integrating network IN, andv a source of alternating current S whose frequency.

is high compared to other frequencies present in the I. S. G. device. By means of phase adjusters, voltage from S' is impressed on the two modulator systems in quadrature phase, while the two input voltages to the device are impressed on each' of the modulators invphase opposition.l The 'ac^' tion of such a pair of balanced modulators is well known and it is therefore sufficient toA state that when the two systems are symmetrically energized and coupled to a common output circuit,

the resulting current in this circuit will be of the frequency of source S but phase modulated to a phase deviation KE. Therefore, it might appear that this current need only be applied to any phase modulation detector toobtain the voltage E. Unfortunately, however, many phase modulation detectors are adapted vto operate only on signals whose phase deviation does not exceed a small value of the order of one radian. In the present case KE may amount to a very large number of radians, so many in fact, as to causeV sult may, however, be cured by passing the frequency modulation detector FM output through an integrating device IN whose output istherefore proportional to the desired voltage E. This integrating device may be of vthe simple lform shown, where the'time constant of the resistor R.

-and condenser C combination is long compared to the period of any component frequency of the voltage E. In this case the current through the combination is substantially equal to the input voltage divided by the resistance, and the voltage drop across the condenser is therefore proportional to the time integral of the input voltage.

A similar result may be obtained by using a con-'- denser for the output impedance of a screen grid amplier stage.

In describing the constitution of the I. S. G.

device, particular forms of balanced modulator and integrating circuit have been shown, but it will be realized that similar results will be obtained from any arrangements adapted to produce from the two input voltages, a high fre- .quency wave'modulated in accordance with E, and

to demodulate such wave to recreate a voltage proportional to E. Although it will be obvious to one skilled in the art. it may be noted that the frequency modulator detector FM, whatever type it be, shown in Fig. 1, should be arranged toreceive the full spectrumnof frequencies of the modulator output, but not a wider range than necessary for such purpose.

Fig. 1 has been described for the purpose of explaining the action of the two inversely behaving devices S. O. G. and I. S. G. The devices would not of course be connected directly together as shown in any practical application. Fig. 2 shows one application of the devices of Fig. 1 and is made a separate figure so that these devices may be indicated in a block diagram, thus avoiding a confusing complication of the diagram of Fig. 2.

Fig. 2, a signaling voltage E is applied through a shaping device SN, whose effect will Abe. neglected for the moment, to an S. O. G. de-

vice such as lis shown at the left in Fig. l. One of the outputs of the S. O. G. is employed to phase modulate a radio transmitter T1 of any desired type. The other output phase modulates another transmitter, T2, operating in a different frequency channel. At the receiving point, separate receivers Rl and R2 reconstruct the output voltages of the S. O. G. and apply them as input voltages to an I. S. G. device such as shown at the right in Fig. 1. In fact, the main difference so far to be noticed between Fig. 2 and Fig. 1 is that Lin Fig. 2 radio links'replace the connections between S. O. G. and I. S. G. indicated by dotted lines in Fig. l. The output of the I. S. G. is passed through a restoring network RN and then applied to a utilization device. As to the shaping and restoring networks SN and RN, neither of these Vare necessary if ,conventional radio transmission is employed, lwhich yields a receiver 'output that is a faithful replica of the transmitter modulating voltage. In case, however, Ti, To are phase modulating transmitters while R1, Raare frequency modulation receivers, then an integrating'A network, such as Vthat shown at IN in Fig. -l, for example, should be employed either as a shaping device SN ahead of theS. O. G., oras a-restoringfdevice RN after the I. S. G. Furthermore, it may be desirable to. employ some sort of shaping device for preemphasizing some characteristic of thesignals, as explained in my copending applicationY Serial No. 475,601, filed February l2, 1943. In such a case'a suitable restoring device will be employed to restore such characteristic' to its original relation to the signal.

A modification vof Fig. 2 which' obviates the necessity of independentchannels for the transmitters is as follows: T1 is a narrow'. phase mod-V ulation transmitter and R1 aY phase modulationreceiver therefor whichisnonrespcnsivfto amplitude modulation... T2 vis'an am'plitudemodulation transmitter and R2 a receivertlirefor which is non-responsive to the modulation 'of T1. Hence T1 and T2 can operate on the same'carrier. ,In

another modification, o'nly'a singletrarsmitter is required, its ,output wave being modulated; in fre-Y quency, for examplejfb'y'cne output'of S. O. G. and in amplitude by the other output lof ,S.' O. G.

In any case, itl willfbe'seen that theV transmission cannot be received on any ordinary receiver since the output of such'receiversjwill be merely a sinusoidalwave generated by thejS. O. G. at the transmitterV and Such Waves 'are'.unintellig'ibleV until reconvertedto the originalfvoltag'e by means of an I: S."G.' device 'such' 'asshowmY In addition to a high degree "of privacy afforded bythe sys-V tem of Fig.` 2', there'isprovided an'improvement in transmission eliiciency due tothe v-fact that each transmitter modul-ationA is of constant maximum -degree therebyprecluding the possibility .of Y

over-,modulation whileat the Sametime maintaining the advantageof full modulationfeven during weak signal periods,

, While I have illustrated one application of the devices explained in Fig. 1, it will be appreciated that they maybe put to a variety of other uses. As an example ofa use for a S. O. G. device in quite a different eld, Fig. 3 shows how an oscilloscope m-ay be used as afvoltmeter to measure Voltage vindependently of any variation in the deflection sensitivityof the electron gun, and-of the amount of, amplication of the voltageto be measured. In Fig. 3 E is `the voltage to be measuredrhere assumed to be periodic although of any waveshape. This Voltage is amplied Vin A toany desired extent and applied to the vertical deflection plate for example, of the oscilloscope S. At the same time, the voltage E is `impressed on a S. O. G, device which for thelpresent purpose` need have only one detecting system and one output voltage, This output voltage is applied to a horizontal deection plate and produces a wiggly trace as shown. Since there are a fixed number of horizontal excursions per volt of E, the peak Voltage of E may be obtained by counting the total number of horizontal excursions visible this number being` independent of the height of the tracewhich latter can be adjusted to any convenient height by adjusting thegain of the amplifier A.

Another general type of application for the S. O. G. is the production, from the output voltages of the S. O. G., of a rotating magnetic or electric field whose angular displacement is proportional to the voltage input to the S. O, G. device. Fig. 4a shows means for producingsuch a rotating magnetic field. The outputs I and 2 of the S. O. G. are preferably adjusted to be in phase quadrature and are applied to eld coil systems which produce, in the region of rotor R. magneticelds at right angles in space. The angular position of the resultant magnetic field is then determined by the input` voltage to the S. ,O. G. The input voltage may be preshaped in SN, ifV desired, to cause the rotating field to depend` in a different way upon the unshaped voltage than has been-stated. ,For example, if the shapingnetwork SN isv arranged to produce an output voltage proportional `to the rate of change of its input voltage, then the angular displacement of the rotary eld will be proportional to rate of change of thevoltage applied to the shaping network, The rotor element` R may be a light transverse permanent magnet whose direction will follow the direction of the resultant eld provided the angular acceleration thereof is not too great. Or the rotor R may be simply a conducting body in which case a torque is developed therein pro-portional to the speed of rotation of the resultant eld.

Fig. 4b shows means to develop a rotary electric eld, or. its equivalent, and apply the same toan oscilloscope The output voltages of an S. `O. Gat l and 2 are connected to the 4vertical ings` the` dotted line marked AVC; indicates that the voltage E is utilized to control the output v o1t age Vofthe ,-S. O. G. Thisispreferably doneas follows: Referring to; Fig. 1, imagine that the last stage of the frequency, multiplier` HG includes a tubehaving a grid whose bias controls the amplitude of 4the frequency multiplied.k output, `for example, a suppressor grid. The. voltage E, or a portion thereof, is then connected so as to vary the bias ofthis grid. Thus when E is small, the oscilloscope spot travels at a Vmedium distance from, the center ofthe screen. AsE becomes morepositivethis distance becomes greater, while as E becomes more negative the distance becomes smaller. VSince the total length of spiral travelled by the spot in one peak to peak swing of a periodic voltage E may be made very much greater than the diameter of the oscilloscope screen, this peak to peak voltage may be read to a correspondingly greater accuracy than in the ordinary use of an oscilloscope as a voltmeter, and furthermore, the voltage reading is entirely independent `of, the constants of the oscilloscope, being dependent only upon the amount of phase deviation in the S. O, G. outputper volt input to the S. O. G.

I claim:

1. The method of deriving, from a rstvoltage, a second voltage which is a sinusoidal function of said rst voltage, which includes` these steps, producing an auxiliary high frequency voltage, phase modulating said high frequency voltage to a high degree in accordance with said rst voltage, and combining said phaseV modulated high frequency` voltage and said high frequency voltage and rectifying said combined voltages.

2. The method recited in claim 1, wherein said high frequency voltage is phase modulated a small amount and said modulated voltage and said high frequency voltage are multiplied in frequency equal amounts before combining and rectifying.

3. The method of deriving, from a rst voltage, two other voltages which are sinusoidal functions of said first voltage, which includes these steps, producing an auxiliary high frequency voltage, phase modulating said high frequency voltage to a high degree in accordance with said rst voltage, separatelycombining two portions of said phase modulated high frequency voltage with two portions of said unmodulated high frequency voltage, the phase relation between the voltages in one of said combinations being made different from that in the other combination and separatelv rectifying the combined voltages.

4. The method as recited in claim 3, wherein the high frequency voltage is phase modulated a small amount and said phase modulated voltages and unmodulated voltages are multiplied equal amounts before being combined.

5. The method of deriving, from a first Voltage, a second and third voltage each of which isa sinusoidal function of said rst voltage and which have a desired phase relation with each other which includes these steps, generating a high frequency voltage, modulating the phase of said high frequency voltage to a high degree in accordance with said first voltage, combining a first portion of said phase modulated high frequency voltage with a first portion of said unmodulated high frequency voltage and rectifying the combined voltage toderive said second voltage, combining a second portion of said phase modulated high'frequency voltage with a` second portion of sadwunmodulated high frequency voltage and rectifying the combined voltage to derive saidthird voltage and adjusting the relative phase ofthe voltages in at least one of the voltage combinations to attain the desired phase relation betweensaid second and third voltages. 6. The method of recovering an original signal from a pair of dissimilar phase voltages each of which is a sinusoidal function of a voltage derived from said signal voltage which includes these steps, producing a high frequency auxiliary wave, Vmodulating said auxiliary high frequency wave in accordance with said pair of sinusoidal voltages .to4V produce a wave which is lphase moldulatedA in accordance with said original signal, detecting' the variations of instantaneous frequency ofthis phaseY modulated high frequency auxiliary wave to derive 'a voltage characteristic 'of said variations and integrating said last named voltage" toobtain'a voltage linearly related to said Vvvoltage derived from said signal voltage.

'7. The rmethod of recovering an original signal from a pair of dissimilar phase voltages each of which is a" sinusoidal function of a voltage derived from said signal voltage which includes these steps, producing a high frequency auxiliary wave, separately modulating each of two phase displaced. portions of said auxiliary high frequency wavefin accordance with said pair of sinusoidal voltages, combining the so modulated waves, detecting the variations of instantaneous frequency of the combined modulated high frequency auxiiiary waves to derive a voltage characteristic of said variations and integrating said last named voltage to obtain a voltage linearly related to said voltage derived from said original signal. v 3. The method of secret signaling which includes these steps, generating a iirstvvoltage characteristic of signals, deriving from said first voltage a Second and a third voltage which are phase displaced vsinusoidal functions of said first voltage, Ymodulating one carrier characteristic with said second voltage and another carrier characteristic with said third voltage, separately detecting said modulations to produce a fourth voltage, and modifying ysaid fourth voltage to vcorrespond tosaid first voltage. f ,9, The method of lsignaling which includes thesestepsLgenerating a rst voltage characteristie of signals, deriving from said first voltage a second voltage which is a sine function of said first voltage, deriving from said first voltage a third voltage which is a cosine function of said first voltage, modulating a carrier in accordance with said second voltage, modulating a second carrier in accordance with said third voltage, transmitting the modulated carriers, receiving the transmitted carriers and demodulating the same to recover voltages corresponding to said second and third voltages, combining the recovered voltages, and deriving from the combined voltages, voltage corresponding to said first voltage. 1

, 10. The method of signaling Whichgincludes these steps, producing a signal voltage, deriving frcmrsaid signal voltage two voltages each of which are sinusoidal functions of said rst voltage, modulating the phase of a first high frequency voltage in accordanceV with one of said two voltages, modulating the phase of a second high Vfrequency Vvoltage in accordance with the other of said two voltages, transmitting said phase modulated voltages, receiving the transrmitted energy, detecting said energy to derive a new voltage, and subjecting said new voltage to correctionso that said new voltage corresponds to said signal voltage.

11. The method of signaling which includes these steps, producing a high frequency voltage, modulatingthe phase of said high frequency voltage in accordance with said signal voltage, mixing modulated high frequency voltages with phase displaced voltages of the frequency of said high frequency voltage, detecting said mixed voltages to derive two new voltages which may be represented by the sine and cosine functions respectively -of said first voltage, transmitting said drived'voltages, differentially modulating phase displaced carriers by the respective derived voltages, combining the differentially modulated carriers, and subjecting the combined energy to a frequency demodulation and integration process to derive the original signal voltage.

l2. In a transmission system of the nature described, a source of signal voltage, means for deriving from said signal voltage a pair of voltages' each of which is a `function of said signal voltage, means for separately transmitting each of said pair of voltages to a receiving point, means at said receiving point for converting said pair of voltages back to said signal voltage and means for utilizing' said recovered signal voltage.

13. In means for deriving from an arbitrarily varying rst voltage, a second voltage which is a harmonic function of the instantaneous value of said first voltage, a source of alternating current-the frequency ofrwhich is high as compared to the said arbitrarily varying first voltage, a phase modulator for strongly phase modulating alternatingcurrent by said first voltage, a rectifier, connections between said rectifier and said phase modulator, connections between said source of alternating current and said rectifier for impressing both said phase modulated current and said unmodulated -current on said rectiler, a phasev adjuster in one of said connections, and a selecting circuit connected to `said rectier for selecting therefrom the voltage corresponding to said second' voltage while rejecting voltage of a frequency equal to that of said source of alternating current and higher.

14, In asystern ofthe class described, a source of signal voltage, means for deemphasizing a characteristic of said signal voltage, means for deriving from the deemphasized signal voltage a pair of voltages each of which is a function of said deemphasized signal voltage, means for separately transmitting each of said pair of voltages I to a receiving point, means at said receiving point for combining said pair of voltages to derive a resultant voltage, and means for restoring a characteristic of said resultant voltage back to its original relation with respect to the said signal voltage.

15. In a signaling system, a source of signal voltage, means for deriving from the signal voltage a pair of voltages .each of which is a function of the signalvoltage, separate means for sending each of the derived voltages to a receiving point, and means at said receiving point for combining said pair of voltages to derive a resultant voltage corresponding to said original signal voltage.

16. In` a signaling system, a source of signals, means coupled to said source for deriving two voltages each of which are sinusoidal functions of saidsignal voltage, separate means for conveying each of the derivedV voltages to a receiving point, andfmeans at said receiving point for combining lated carrier to a receiving point, at the receiving point demodulating the carrier to derive a, voltage corresponding to said resultant voltage, and deriving from the resultant voltage a voltage cor- ,5 responding to the signal voltage.

WALTER VAN B. ROBERTS. 

